1. Field of the Invention
The present invention relates to an auxiliary braking system. More specifically, the present invention relates to an auxiliary braking system for a vehicle equipped with a transmission having a forward clutch and a reverse clutch.
2. Background Information
Industrial-use vehicles, such as forklifts, are usually equipped with a torque converter to which torque is transmitted from an engine side and a transmission to which torque is transmitted from the torque converter. The transmission has a forward clutch and a reverse clutch and outputs torque to the output shaft by engaging one or the other of these clutches. When the brakes are applied in such a forklift, a foot brake is depressed causing a drum brake to operate and braking the travel of the vehicle.
In general, braking frequency is higher for forklifts and other industrial-use vehicles than for ordinary vehicles. Furthermore, since the drum brakes of forklifts only operate on the front wheels, a large burden is placed on the drum brakes. Consequently, the wear of the lining of the drum brakes is severe and the service life of the brakes is shortened.
Moreover, since many industrial-use vehicles use a torque converter, the frequency of foot brake use is higher because engine braking is not very effective even when the driver releases his or her foot from the accelerator pedal to disengage engine throttle. In particular, when a divided stator torque converter is used, the gear ratio (speed ratio) is small compared to torque converters that do not have a divided stator and engine braking is even less effective.
As discussed, since it is difficult to utilize engine braking in conventional forklifts and other industrial-use vehicles, the life of the foot brake is short and it is difficult to reduce the work cycle time, making work efficiency poor.
In view of these issues, a hydrostatic transmission (HST) that uses a hydraulic pump and a hydraulic motor has already been proposed. When an HST is used, it is possible to achieve a braking effect similar to that of engine braking by controlling the hydraulic pressure that acts on the hydraulic motor. However, a conventional HST system is expensive and its efficiency is relatively low. Thus, there are still issues remaining to be solved regarding the use of this method in actual practice.
In view of the above, there exists a need for a vehicle auxiliary braking system that overcomes the above-mentioned problems in the prior art. This invention addresses this need in the prior art as well as other needs, which will become apparent to those skilled in the art from this disclosure.
An object of the present invention is to provide inexpensively a braking effect similar to engine braking for industrial use vehicles. Another object of the present invention is to extend the life of the brakes by reducing the load that acts on the brakes. Another object of the present invention is to reduce the work cycle time in order to improve work efficiency.
A vehicle auxiliary braking system for use in a vehicle equipped with a transmission having a forward clutch and a reverse clutch in accordance with a first aspect of the present invention has a travel detection means, an accelerator depression detection means, and a braking clutch engaging means. The travel detection means detects whether the vehicle is traveling at or above a prescribed speed. The accelerator depression detection means detects whether the depression amount of the vehicle accelerator is at or below a prescribed depression amount. The braking clutch engaging means engages the clutch that corresponds to the opposite travel direction when the detection results from the travel detection means and accelerator depression detection means indicate that the vehicle is traveling at or above the prescribed speed and the accelerator depression amount is at or below the prescribed depression amount.
With this system, when the accelerator depression amount goes below the prescribed depression amount while the vehicle is traveling, the braking clutch engaging means engages the clutch corresponding to the opposite travel direction based on the detection results from the travel detection means and the accelerator depression detection means. Consequently, a braking effect similar to engine braking can be expected. As a result, the load on the main brake is reduced and the life of the main brake is lengthened. Since travel resulting from momentum is suppressed, the work cycle time can be shortened and the work efficiency improves. Low cost can also be achieved because the system can be accomplished without adding brake linings or other additional members to the brakes.
A vehicle auxiliary braking system in accordance with a second aspect of the present invention is the system of the first aspect, wherein the forward clutch and reverse clutch are both hydraulic clutches. Further, the braking clutch engaging means selectively supplies a prescribed braking hydraulic pressure to the forward clutch and reverse clutch.
In this system, the clutches are hydraulic. Thus, the braking force can be controlled easily by controlling the hydraulic pressure. Additionally, heating that occurs when the brakes are applied can be suppressed easily by securing a sufficient amount of lubricating oil.
A vehicle auxiliary braking system in accordance with a third aspect of the present invention is the system of the second aspect, wherein the accelerator depression detection means detects whether or not the accelerator pedal is being depressed.
With this system, engine braking occurs whenever the driver releases his or her foot from the accelerator pedal. Consequently work efficiency is improved even further.
A vehicle auxiliary braking system in accordance with a fourth aspect of the present invention is the system of the second or third aspect, wherein the travel detection means has a centrifugal element and a travel detection hydraulic circuit. The centrifugal element is acted upon by a centrifugal force when the output shaft of the vehicle rotates. The travel detection hydraulic circuit drains the hydraulic oil that is being directed to the forward clutch and the reverse clutch of the braking clutch engaging means by the centrifugal element moving outward due to centrifugal force.
Since this system utilizes a mechanical means to detect whether or not the vehicle is traveling, it is possible to construct the system inexpensively relative to those systems that detect and control using a microcomputer or the like.
A vehicle auxiliary braking system in accordance with a fifth aspect of the present invention is the system of any of the second to fourth aspects, wherein the braking clutch engaging means also has a regulator valve for adjusting the braking hydraulic pressure supplied to the forward clutch and the reverse clutch.
Since this system adjusts the braking hydraulic pressure using a regulator valve, the braking force can be adjusted easily and the most efficient braking force can be obtained for a variety of vehicle specifications.